The growfs utility extends the
newfs(8) program. Before starting
growfs, the partition must be set to a larger
size using disklabel(8). The
growfs utility extends the size of the file
system on the specified special file.

Currently growfs can only enlarge unmounted file
systems. Do not try enlarging a mounted file system - your system may panic
and you will not be able to use the file system any longer. Most of the
newfs(8) options cannot be
changed by growfs. In fact, you can only increase
the size of the file system. Use
tunefs(8) for other changes.

Determines the size of the
file system after enlarging in sectors. This value defaults to the size of
the raw partition specified in special
(in other words, growfs will enlarge the file
system to the size of the entire partition).